This invention relates to a novel and improved filter press, and more particularly to a filter press which permits reduction in scale of hydraulic cylinder means for tightening a plurality of movable frame members consisting of filter plates or filter plates and filter frame even when the press is enlarged in scale for enlarging filtering capacity.
There has been known to the art a filter press of the type in which a plurality of movable frame members are arranged between a pair of heads with at least one filter cloth supported between adjacent frame members and in which one of the heads is movably supported so that the movable head may be advanced and retracted by hydraulic cylinder means for tightening the frame members. The filtering operation is carried out when the heads are closest to each other so that the frame members are tightened, and the cakes-discharging operation is carried out when the heads are separated from each other.
Filter presses of the above type are shown in, for example, U.S. Pat. Nos. 3,618,782; 3,698,557; and 3,807,567. In the filter press disclosed in U.S. Pat. No. 3,618,782, alternately arranged filter frames and filter plates are employed as the mentioned movable frame members and an endless filter cloth is entrained over guide rollers arranged above and below the filter plates in a zig-zag fashion so that the cloth is disposed between each adjacent filter frame and filter plate. In the filter press disclosed in U.S. Pat. No. 3,698,557, alternately arranged filter frames and filter plates are also employed as the mentioned movable frame members and a pair of endless filter cloths are provided to each of the filter plates by entraining the same over guide rollers arranged above and below each filter plate. Further, in the filter press disclosed in U.S. Pat. No. 3,807,567, recessed filter plates are employed as the movable frame members and a pair of filter cloths between which slurry to be filtered is to be supplied are disposed between each two adjacent filter plates so that the cloths may be travelled downwardly during the cakes-discharging operation. The most important advantage of such filter press is that the cakes-discharging operation is very easy and time-saving because all of the filter cakes on the filter cloth can be discharged or removed so as to clean the cloth at the same time by travelling the cloth in a manner in which the frame members are separated to give definite intervals therebetween.
In the foregoing filter press as of the prior art, the mentioned hydraulic cylinder means for tightening the movable frame members is also used as means for assembling and separating the frame members, namely for advancing and retracting the frame members. In this case, the cylinder means is required to have not only a large driving force but a large stroke. In particular, when the number of the frame members and the filtering area of each filter plate are increased for enlarging the filtering capacity of the filter press according to the recent demand on the filter press, a hydraulic cylinder means for moving and tightening the frame members having a very large stroke and a very large driving force is required. Further, in such filter press, diaphragms of an elastic material for pressing filter cakes so as to dewater the same are often employed which are disposed on the surfaces of the filter plates and into which fluid is supplied under pressure so as to expand the diaphragms for pressing the cakes after a filtering operation as shown, by way of example, in U.S. Pat. No. 3,807,567. In such case, a hydraulic cylinder means for tightening the frame members having a very large driving force is required for bearing the high pressure of the fluid for expanding the diaphragms. Thus, the hydraulic cylinder unit for moving and tightening the frame members is necessarily designed so that it has a large scale, requires a large space for the cylinder means, and has a large manufacturing cost. In particular, the piston rod of such cylinder means must have a large diameter for providing strength against buckling of the long piston rod which receives a large pressure or force and increases the manufacturing cost. Although the length or span of such cylinder means may be shortened by employing a telescopically extensible cylinder unit, such telescopically extensible cylinder unit requires a very large manufacturing cost.